Refining of molten metal

ABSTRACT

A method of refining molten metal, especially steel, utilizes improved apparatus for injecting gaseous treating media such as oxygen into the molten metal. The apparatus is provided with an internally-cooled nozzle that directs the gaseous medium into the molten bath and that is fabricated of an improved copper alloy to thereby significantly reduce the frequency of required apparatus replacement during the metallurgical processing.

United States Patent lnventor Herbert Greenewald, Jr

Upper Arlington, Ohio Appl. No. 877,872

Filed Nov. 18, 1969 Patented Nov. 9, 1971 Assignee Berry Metal Company Harmony, Pa.

REFINING OF MOLTEN METAL 12 Claims, No Drawings US. Cl. 75/60, I 75/76, 75/93, 266/34 L Int. Cl CZlc 5/28, C22b 9/00 Field of Search 75/59, 60, 153, 162.93, 76; 266/34 L;239/132,3. 132.5

References Cited UNITED STATES PATENTS l/l962 Saarivirta 75/l53 3,20l,l04 8/l965 Berry 75/60X 3,3 l0,393 3/l967 Cogen 75/60 3,338,570 8/1967 Zimmerm. 266/34 L 3,529,955 9/1970 Themelis 75/60 Primary I;I\'aminer L. Dewayne Rutledge Assistant Examiner-G. K. White A!l0rneyDaniel H. Dunbar REFINING OF MOLTEN METAL SUMMARY OF THE INVENTION Otherwise conventional metallurgical apparatus such as lances for basic oxygen and open hearth furnaces and tuyeres for blast furnaces are provided with internally cooled nozzles fabricated of copper alloyed with zirconium in the approximate range from 0.005 percent to 0.03 percent by weight in combination with aluminum in a like or even greater amount. When alloyed properly under vacuum conditions or in a metallurgically inert gaseous environment, the alloyed metal of the nozzles develops improved resistance to embrittlement at grain boundary regions and in terms of prolonged tensile stress of 4,000 p.s.i. to 5,000 p.s.i. magnitude at temperatures in the range of 900 F. to l,000 F. is less likely to exhibit surface cracking and flaking or erosion failure under typical metal refining conditions. Analyses of nozzles that have failed in the specified manners suggests that the principal metallurgical phenomenum contributing to failure is a form of embrittlement accompanied by subsequent preferential oxidation or sulfidation attack at the near-continuous iron-rich and possibly chromium-rich zones associated with the embrittlement.

DETAILED DESCRIPTION Water-cooled copper nozzles or tips utilized in metallurgical lance equipment of the type detailed in U.S. Pats. Nos. 3,118,608 and 3,201,104 (each in the name of W. V. Berry) or discussed from a metallurgical processing standpoint in U.S. Pat. No. 3,310,393 (issued in the name of L. L. Cogan), by way of example, are used extensively in steelmaking processes for injecting oxygen and other gases or even solids into molten metal contained in basic oxygen furnace equipment and the like. In such service the watercooled side of the copper remains at near-water temperatures and the face of the copper next to the molten steel bath is believed to reach temperatures in the 700 F. to 1,000 F. range.'Such higher temperature constantly varies with furnace conditions and with the position of the lance assembly in the furnace as it is lowered into the furnace for blowing or elevated or retracted for pouring or charging. As the face of the nozzle or tip thermally cycles, it is heated to the temperature range cited and as a result of the heating in combination with the necessary water cooling of the inner surface the hot surface of the tip is alternately subjected to tensile and compressive stresses.

As a result of the combination of elevated temperatures and stresses, the surface of the copper develops cracks along grain boundaries and as the cracks progress inwards either one or both of two modes of failure occur; either mode can eventually end the service life of the nozzle or tip. One mode of failure is that the cracks may extend to the internal water passageways causing water to leak into the furnace interior. The other mode of failure is such that the cracking along grain boundaries loosens grains of copper in the vicinity of the nozzle surface and at the elevated temperatures thereby causing surface metal to flake off. Such flaking or erosion causes the nozzle shape to change and often eventually destroys the effectiveness of the jetted oxygen stream in the molten steel bath.

Investigation has shown that the noted intergranular cracking is principally a form of metallurgical embrittlement involving the preferential precipitation of iron-rich and also possibly chromium-rich material at grain boundary regions of the copper in forms of a near-continuous film either alone or with subsequent preferential oxidation or sulfidation attack on such iron and/or chromium enriched zones. The copper investigated was essentially high-purity copper containing only a few parts per million (by weight) of most impurities, and in particular a near-trace iron content generally not in excess of 50 parts per million by weight.

It has been discovered that the onset of such failure by embrittlement can be significantly delayed in the stressed and heated copper part, particularly at elevated temperatures where the iron-rich and chromium-rich materials diffuse more rapidly, by the controlled combining of zirconium and aluminum into the copper in minimum amounts that are stoichiometrically related to the iron (and possibly chromium, if any) content of the copper. Although additions of the specified zirconium and aluminum alloying elements to the copper in amounts greater than the preferred range may not reduce the embrittlement delay that is otherwise obtained, and sometimes may even somewhat enhance the improvement, the increased amounts may have an adverse effect on other properties such as reducing electrical conductivity.

For the purpose of this invention it is preferred that the amount of zirconium added he in the range of 0.005 percent to 0.03 percent by weight of the total alloy. in many instances the amount of zirconium alloyed into the copper to obtain the advantages associated with this invention is in the narrower range of approximately 0.01 percent to 0.02 percent by weight of the total alloy.

The amount of aluminum to be alloyed into the same copper in the practice of this invention is essentially like the amount of zirconium although proportionally larger amounts of aluminum, within limits, do not appear to adversely affect the delay in onset of embrittlement that otherwise is obtained. Thus, the invention also preferably involves the addition of a corresponding amount of aluminum in the range of approximately from 0.005 percent to 0.03 percent by weight to the copper and often an amount in the range from 0.01 percent to 0.02 percent is utilized. No clear upper limit for the aluminum content is known and in at least one instance a total of 0.3 percent aluminum has been employed with a 0.02 percent zirconium addition.

It is also important in the practice of the instant invention I that the alloying elements be combined with the copper in a controlled manner. In one such acceptable method of alloying the copper is vacuum melted, deoxidized by hydrogen-bub bling in a partial vacuum, combined with the alloying elements under a vacuum condition, thoroughly mixed by argon bubbling in a partial vacuum, and afterwards also cast and solidified under vacuum. In an alternate acceptable method deoxidized copper is melted, alloyed, mixed, and cast and solidified entirely in a nonreactive gaseous environment such as in essentially pure argon. Exposure of the alloying elements to oxygen at metal-melting temperatures must be avoided. Also, alloying conditions should be such that the zirconium and aluminum additions not be in an oxide, nitride, or carbide form or their effectiveness will not be realized. Accordingly, it is preferred that the specified alloying ingredients be combined in their metallic form. Although not presently known, it is conjectured that homologues of the alloying elements, particularly hafnium, are operative to obtain the advantages of the instant invention.

The comparative data in the following tables l and II illustrates the significance of the instant invention with respect to effecting a delay in the onset of embrittlement under conditions of tensile stress and elevated temperatures. Table I provides information regarding the improved alloys; table II, on the other hand, relates to coppers alloyed in a conventional manner. In each case, however, the alloyed metal tested was prepared in a manner involving deoxidation and was subjected in tensile bar form, to a tensile stress of at least 4,000 p.s.i. and

a temperature of approximately 950 F. The time to embrittlement (rupture) under the specified test conditions is given for each of the representative melt alloy compositions indicated.

p.s.i. tensile stress; bar failed on subsequent loading to 7,000

In the foregoing tables, amounts given as zero were unmeasurable and are essentially considered to'be nil or less than trace amounts (less than approximately 50 parts per million by weight). The iron content of each alloy in each instance was determined to be less than 30 parts per million (less than 0.003 percent) by weight, such amount determinations being derived from spectrographic analyses.

I claim:

1. In a method of refining molten metal, the step of directionally injecting a treating medium into the molten metal through an internally cooled nozzle fabricated of a copper alloy comprised on a weight basis of approximately from 0.005 percent to 0.03 percent zirconium, at least approximately from 0.005 percent to 0.03 percent aluminum, and the balance except for impurities deoxidized copper.

2. The invention defined by claim 1, wherein the zirconium and aluminum contents are each approximately from 0.005 percent to 0.01 percent.

3. The invention defined by claim 1, wherein the zirconium content is approximately 0.005 percent and the aluminum content is approximately 0.01 percent.

4. The invention defined by claim 1, wherein the zirconium content is approximately 0.02 percent and the aluminum content is approximately 0.3 percent.

5. The invention defined by claim 1, wherein the zirconium is combined in the copper alloy with iron to form a stable intermetallic compound.

6. The invention defined by claim 5, wherein the zirconium is combined in the copper alloy with aluminum and iron to form a stable ternary system intermetallic compound.

7. In apparatus for use in refining molten metal, in combination:

a. nozzle body means;

b. a through-opening in said nozzle body means for directionally injecting a treating medium into molten metal; and

c. internal passageways in said nozzle body means for circulating a coolant,

said nozzle body means being fabricated of a copper alloy comprised on a weight basis of approximately from 0.005 percent to 0.03 percent zirconium, at least approximately from 0.005 percent to 0.03 percent aluminum, and the balance except for impurities deoxidized copper.

8. The invention defined by claim 7, wherein the zirconium and aluminum contents are each approximately from 0.005 percent to 0.01 percent.

9. The invention defined by claim 7, wherein the zirconium content is approximately 0.005 percent and the aluminum content is approximately 0.01 percent.

10. The invention defined by claim 7, wherein the zirconium content is approximately 0.02 percent and the aluminum content is approximately 0.3 percent.

11. The invention defined by claim 7, wherein the zirconium is combined in the copper alloy with iron to form a stable intermetallic compound.

12. The invention defined by claim 11, wherein the zirconium is combined in the copper alloy with aluminum and iron to form a stable ternary system intermetallic compound. 

2. The invention defined by claim 1, wherein the zirconium and aluminum contents are each approximately from 0.005 percent to 0.01 percent.
 3. The invention defined by claim 1, wherein the zirconium content is approximately 0.005 percent and the aluminum content is approximately 0.01 percent.
 4. The invention defined by claim 1, wherein the zirconium content is approximately 0.02 percent and the aluminum content Is approximately 0.3 percent.
 5. The invention defined by claim 1, wherein the zirconium is combined in the copper alloy with iron to form a stable intermetallic compound.
 6. The invention defined by claim 5, wherein the zirconium is combined in the copper alloy with aluminum and iron to form a stable ternary system intermetallic compound.
 7. In apparatus for use in refining molten metal, in combination: a. nozzle body means; b. a through-opening in said nozzle body means for directionally injecting a treating medium into molten metal; and c. internal passageways in said nozzle body means for circulating a coolant, said nozzle body means being fabricated of a copper alloy comprised on a weight basis of approximately from 0.005 percent to 0.03 percent zirconium, at least approximately from 0.005 percent to 0.03 percent aluminum, and the balance except for impurities deoxidized copper.
 8. The invention defined by claim 7, wherein the zirconium and aluminum contents are each approximately from 0.005 percent to 0.01 percent.
 9. The invention defined by claim 7, wherein the zirconium content is approximately 0.005 percent and the aluminum content is approximately 0.01 percent.
 10. The invention defined by claim 7, wherein the zirconium content is approximately 0.02 percent and the aluminum content is approximately 0.3 percent.
 11. The invention defined by claim 7, wherein the zirconium is combined in the copper alloy with iron to form a stable intermetallic compound.
 12. The invention defined by claim 11, wherein the zirconium is combined in the copper alloy with aluminum and iron to form a stable ternary system intermetallic compound. 